This invention relates to a process for making sealing gaskets by deposition and subsequent curing of elastomeric polymers and the like. The invention is also concerned with the gasket itself as obtained by such process.
Conventional methods of gasket manufacture substantially comprise either punching the gasket out of a (possibly many-layered) sheet material, or shape the gasket by injection-moulding of an elastomeric mix or the like. With both of these methods, but especially with injection moulding, expensive tools (punches and moulds) are required, and this is reflected in a high cost of the gaskets themselves, particularly if only relatively small quantities of such gaskets are to be manufactured.
More recently, new manufacturing methods have been developed, whereby a thread of a fluid elastomer is deposited from a nozzle onto a flat non-adhesive support, e.g. a semirigid sheet of a material such as PVC, following the outline of the gasket, and subsequently the fluid elastomer is cured, either at ambient temperature or in an oven, with or without accelerators or other addities. The nozzle is displaced by numerical control pantograph devices or the like, and it runs along two horizontal coordinates, parallelly to the plane of the support sheet, while depositing on it a thread of elastomer or other suitable resin. The gasket so obtained is often supplied to the end user while still sticking (with a weak adhesion) to the support sheet itself, to be peeled away before use.
The above manufacturing process by deposition of a fluid polymer gives rise to gaskets that can often be used as replacements for injection-moulded gaskets, with definitely lower tooling costs, particularly in the case of gaskets having an intricate pattern. However, such process was limited to flat gaskets, while for tridimensional gaskets only injection-moulding has been used.
Even more recently, manufacturers of end products such as engines, motorcars and the like, in order to reduce costs of seals between surfaces, have in some cases dispensed with a gasket altogether, and have instead resorted to the expedient of depositing a thread of an elastomer directly on the surface of the part, the thread-producing nozzle being displaced by means of numerical control devices capable of moving along three coordinates. Costs have thereby been reduced in the original equipment, but a problem has arisen with spare parts, because the same method cannot be used there and, on the other hand, the high cost of injection-moulding discourages manufacturers from tooling up in order to supply the spare part market alone. Therefore, operators in these cases have had to overcome the difficulty by manually depositing a fresh thread of elastomer on the part. This approach is unsatisfactory, because manual deposition is time-consuming and requires an appreciable degree of expertise, while the quality of the result in each case depends critically on the operator's manual skill.